JP7779804B2 - Electrode mixture, electrode active material layer, and lithium ion battery - Google Patents

Description

This disclosure relates to an electrode mixture, an electrode active material layer, and a lithium-ion battery.

Patent Document 1 discloses an all-solid-state lithium ion secondary battery, characterized in that the negative electrode contains negative electrode active material particles, a conductive material, and a solid electrolyte, the negative electrode active material particles contain at least one active material selected from the group consisting of elemental Si and SiO, and the BET specific surface area of the negative electrode active material particles is in the range of 1.9 ^{m 2} /g or more and 14.2 ^{m 2} /g or less.

Patent Document 2 discloses an all-solid-state lithium ion secondary battery, characterized in that the anode contains anode active material particles, a conductive material, and a solid electrolyte, the anode active material particles contain at least one active material selected from the group consisting of elemental Si and SiO, and the anode active material particles have a value A calculated by the following formula (1) in the range of 6.1 to 54.8:
A=S _BET ×d _med ×D (1)
(In the above formula (1), SBET represents the BET specific surface area (m ² /g) of the negative electrode active material particles, d _med represents the median diameter D50 (μm) of the negative electrode active material particles, and D represents the density (g/cm ³ ) of the negative electrode active material particles.)

Non-Patent Document 1 states that when a specific polymer electrolyte is mixed with a sulfide solid electrolyte, the polymer electrolyte and the sulfide solid electrolyte may react and deteriorate.

Japanese Patent Application Laid-Open No. 2019-16517 Japanese Patent Application Laid-Open No. 2019-16516

Nathalie Riphaus et al, ''Understanding Chemical Stability Issues between Different Solid Electrolytes in All-Solid-State Batteries'', Journal of The Electrochemical Society, 166 (6) A975-A983 (2019)

The present disclosure aims to provide an electrode composite that can improve the discharge capacity of all-solid-state batteries.

The present inventors have found that the above object can be achieved by the following means:
Aspect 1
The electrode mixture contains an electrode active material that expands and contracts with charging and discharging, a polymer electrolyte having a monomer unit derived from a norbornene and a monomer unit derived from a maleic anhydride, and a sulfide solid electrolyte.
Aspect 2
2. The electrode mixture according to claim 1, wherein the molar ratio of the monomer units derived from maleic anhydrides to the monomer units derived from norbornenes in the polymer electrolyte is 40 to 60%.
Aspect 3
3. The electrode mixture according to claim 1, wherein the polymer electrolyte has an average molecular weight of 5,000 to 50,000.
Aspect 4
The electrode mixture according to any one of aspects 1 to 3, wherein the ratio of the mass of the polymer electrolyte to the total mass of the polymer electrolyte and the sulfide solid electrolyte is 10.0 to 40.0 mass%.
Aspect 5
An electrode active material layer containing the electrode mixture according to any one of aspects 1 to 4.
Aspect 6
A lithium ion battery having a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer stacked in this order,
At least one of the positive electrode active material layer and the negative electrode active material layer is the electrode active material layer according to aspect 5.
Lithium-ion battery.
Aspect 7
7. The lithium ion battery of claim 6, wherein the solid electrolyte layer comprises a sulfide solid electrolyte.
Aspect 8
A lithium ion battery according to aspect 6 or 7, wherein the electrode active material contained in the electrode active material layer has a maximum expansion/contraction rate of 105% or more during charging and discharging when the lithium ion battery is in use.

This disclosure provides an electrode composite that can improve the discharge capacity of all-solid-state batteries.

FIG. 1 is a schematic diagram showing a state in which a negative electrode active material layer 14 according to the first embodiment of the present disclosure is formed on a negative electrode current collector layer 15. FIG. 2 is a schematic diagram of a lithium-ion battery 1 according to a first embodiment of the present disclosure.

Embodiments of the present disclosure are described in detail below. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the disclosure.

《Electrode composite material》
The electrode mixture of the present disclosure contains an electrode active material that expands and contracts with charge and discharge, a polymer electrolyte having a monomer unit derived from a norbornene and a monomer unit derived from a maleic anhydride, and a sulfide solid electrolyte.

Here, "electrode active material that expands and contracts with charge and discharge" refers to an electrode active material that expands and contracts by absorbing and releasing charge carriers, such as lithium ions in a lithium-ion battery, with the charging and discharging of the battery; in other words, the particle size increases and decreases.

In batteries (particularly all-solid-state batteries) containing such electrode active materials, the expansion and contraction of the electrode active material in the electrode active material layer during charging and discharging can cause cracks in the electrode active material layer and/or create voids between the electrode active material and the solid electrolyte.

Cracks in the electrode active material layer or the occurrence of voids between the electrode active material and the solid electrolyte can result in a decrease in battery capacity.

The electrode mixture disclosed herein contains, in addition to an electrode active material and a sulfide solid electrolyte that expand and contract during charging and discharging, a polymer electrolyte having monomer units derived from norbornenes and monomer units derived from maleic anhydrides.

Polymer electrolytes containing monomer units derived from norbornenes and monomer units derived from maleic anhydrides have significantly lower rigidity than solid electrolytes. Therefore, an electrode active material layer formed using an electrode mixture containing this polymer electrolyte and an electrode active material that expands and contracts with charge and discharge can absorb the expansion and contraction of the electrode active material in the electrode active material layer that occurs during charge and discharge by the deformation of the polymer electrolyte. This can prevent cracking of the electrode active material layer and the occurrence of voids between the electrode active material and the solid electrolyte.

Therefore, the electrode composite of the present disclosure can suppress cracking of the electrode active material layer and the occurrence of voids between the electrode active material and the sulfide solid electrolyte due to the polymer electrolyte, while also providing high charge carrier conductivity due to the sulfide solid electrolyte.

As described in Non-Patent Document 1, when a specific polymer electrolyte is mixed with a sulfide solid electrolyte, the polymer electrolyte and the sulfide solid electrolyte may react and deteriorate.

In this regard, the polymer electrolyte containing monomer units derived from norbornenes and monomer units derived from maleic anhydrides used in the electrode mixture of the present disclosure has low reactivity with sulfide solid electrolytes.

As a result, batteries having electrode active material layers containing the electrode mixture of the present disclosure have improved discharge capacity.

In addition to the electrode active material that expands and contracts during charging and discharging, the polymer electrolyte having monomer units derived from norbornenes and monomer units derived from maleic anhydrides, and the sulfide solid electrolyte, the electrode mixture of the present disclosure may optionally contain other components, such as a binder and/or a conductive additive.

<Electrode active material>
The electrode mixture of the present disclosure contains an electrode active material that expands and contracts during charge and discharge.

The electrode active material may be either a positive electrode active material or a negative electrode active material.

Examples of positive electrode active materials that expand and contract during charge and discharge include sulfur-based active materials. The sulfur-based active material is an active material containing at least the element S. The sulfur-based active material may or may not contain the element Li. Examples of sulfur-based active materials include elemental sulfur, lithium sulfide (Li ₂ S), and lithium polysulfide (Li ₂ S _x , 2≦x≦8).

Examples of negative electrode active materials that expand and contract during charging and discharging include Si or Sn, or alloy-based active materials. Examples of alloy-based active materials include Si alloy-based negative electrode active materials and Sn alloy-based negative electrode active materials. Examples of Si alloy-based negative electrode active materials include silicon, silicon oxide, silicon carbide, silicon nitride, and solid solutions thereof. Si alloy-based negative electrode active materials may also contain elements other than silicon, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, or Ti. Examples of Sn alloy-based negative electrode active materials include tin, tin oxide, tin nitride, and solid solutions thereof. Sn alloy-based negative electrode active materials may also contain elements other than tin, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Ti, or Si. Of these, Si alloy-based negative electrode active materials are preferred.

<Polymer electrolyte>
The electrode mixture of the present disclosure contains a polymer electrolyte having a monomer unit derived from a norbornene and a monomer unit derived from a maleic anhydride.

Here, the monomer unit derived from norbornenes is represented by the following structural formula (1):

In structural formula (1), R ₁ , R ₂ , R ₃ , and R ₄ are, for example, each independently a hydrogen atom or a group selected from the group consisting of an alkyl group having 1 to 6 carbon atoms, an alkenyl group, an alkynyl group, and an aryl group.

In structural formula (1), a monomer unit in which R ₁ , R ₂ , R ₃ , and R ₄ are all hydrogen atoms, i.e., a monomer unit derived from norbornene, is a monomer unit derived from norbornene, i.e., 2-norbornenebicyclo[2.2.1]hept-2-ene, and is represented by the following structural formula (2):

The monomer unit derived from maleic anhydrides is represented by the following structural formula (3):

In structural formula (3), R ₅ and R ₆ are, for example, each independently a hydrogen atom or a group selected from the group consisting of an alkyl group having 1 to 6 carbon atoms, an alkenyl group, an alkynyl group, and an aryl group.

In structural formula (3), when _R5 and _R6 are both hydrogen atoms, the monomer unit is derived from maleic anhydride and is represented by the following structural formula (4):

The molar ratio of monomer units derived from maleic anhydrides to monomer units derived from norbornenes in the polymer electrolyte may be 40 to 60%.

The molar ratio of monomer units derived from maleic anhydrides to monomer units derived from norbornenes in the polymer electrolyte may be 40% or more, 42% or more, 44% or more, or 46% or more, and may be 60% or less, 58% or less, 56% or less, or 54% or less.

The average molecular weight of the polymer electrolyte may be 5,000 to 50,000. Note that the average molecular weight is the weight average molecular weight.

The average molecular weight of the polymer electrolyte may be 5,000 or more, 6,000 or more, 7,000 or more, or 8,000 or more, and may be 50,000 or less, 40,000 or less, 30,000 or less, or 20,000 or less.

The ratio of the mass of the polymer electrolyte to the total mass of the polymer electrolyte and sulfide solid electrolyte is preferably 10.0 to 40.0 mass%.

The ratio of the mass of the polymer electrolyte to the total mass of the polymer electrolyte and the sulfide solid electrolyte may be 10.0 mass% or more, 15.0 mass% or more, or 20.0 mass% or more, and may be 40.0 mass% or less, 35.0 mass% or less, or 30.0 mass% or less.

<Sulfide solid electrolyte>
The electrode mixture of the present disclosure contains a sulfide solid electrolyte.

Examples of sulfide solid electrolytes include, but are not limited to, sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, and argyrodite-type solid electrolytes. Specific examples of sulfide solid electrolytes include Li ₂ S—P ₂ S ₅ systems (Li ₇ P ₃ S ₁₁ , Li ₃ PS ₄ , Li ₈ P ₂ S ₉ , etc.), Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ , LiI—Li ₂ S—P ₂ S ₅ , LiI—LiBr—Li ₂ S—P ₂ S ₅ , Li ₂ S—P ₂ S ₅ —GeS ₂ (Li ₁₃ GeP ₃ S ₁₆ , Li ₁₀ GeP ₂ S _{12 ,} etc.), LiI—Li ₂ S—P ₂ O ₅ , LiI—Li ₃ PO ₄ —P ₂ S ₅ , Li _7-x PS _6-x Cl _x, etc.; or combinations thereof.

The sulfide solid electrolyte may be glass, glass ceramic, or a crystalline material. Glass can be obtained by amorphous processing of a raw material composition (e.g., a _mixture of _Li2S and _P2S5 ). Examples of amorphous processing include mechanical milling. Mechanical milling may be dry mechanical milling or wet mechanical milling, with the latter being preferred. This is because it can prevent the raw material composition from adhering to the wall surface of a container or the like. Glass ceramics can be obtained by heat treating glass. Crystalline materials can be obtained, for example, by solid-phase reaction processing of the raw material composition.

The sulfide solid electrolyte is preferably in the form of particles. The sulfide solid electrolyte has an average particle size (D50) of, for example, 0.01 μm or more. On the other hand, the sulfide solid electrolyte has an average particle size (D50) of, for example, 10 μm or less, or may be 5 μm or less. The sulfide solid electrolyte has a lithium ion conductivity at 25° C. of, for example, 1×10 ⁻⁴ S/cm or more, and preferably 1×10 ⁻³ S/cm or more.

<Binder>
The electrode mix of the present disclosure can optionally contain a binder.

The binder may be, for example, but is not limited to, materials such as polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), butadiene rubber (BR), or styrene butadiene rubber (SBR), or combinations thereof.

<Conductive additive>
The conductive additive may be a known material, such as a carbon material or metal particles. Examples of the carbon material include at least one material selected from the group consisting of carbon black (e.g., acetylene black or furnace black), vapor-grown carbon fiber (VGCF), carbon nanotubes, and carbon nanofibers. From the viewpoint of electron conductivity, at least one material selected from the group consisting of VGCF, carbon nanotubes, and carbon nanofibers may be used. Examples of the metal particles include nickel, copper, iron, and stainless steel particles.

《Electrode active material layer》
The electrode active material layer of the present disclosure contains the electrode mixture of the present disclosure.

The electrode active material layer of the present disclosure may be, for example, a layer of the electrode mixture of the present disclosure.

The electrode active material layer of the present disclosure can be formed, for example, by placing a slurry of the electrode mixture of the present disclosure on a substrate such as a current collector layer and drying it.

Figure 1 is a schematic diagram showing a negative electrode active material layer 14 formed on a negative electrode current collector layer 15 according to the first embodiment of the present disclosure.

Lithium-ion battery
The lithium-ion battery of the present disclosure is a lithium-ion battery in which a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer are stacked in this order, and at least one of the positive electrode active material layer and the negative electrode active material layer is the electrode active material layer of the present disclosure. Note that a battery in which a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer are stacked in this order, such as the lithium-ion battery of the present disclosure, is also called an all-solid-state battery. Note that the lithium-ion battery of the present disclosure may further include a positive electrode current collector layer and a negative electrode current collector layer.

Here, the solid electrolyte layer of the lithium-ion battery disclosed herein may also contain a sulfide solid electrolyte.

Furthermore, it is preferable that the electrode active material contained in the electrode active material layer has a maximum expansion/contraction rate of 105% or more during charging and discharging when the lithium ion battery is in use.

Here, the maximum expansion/contraction rate is the ratio of the particle diameter of the electrode active material when it expands the most to the particle diameter of the electrode active material when it shrinks the most during charging and discharging of a lithium-ion battery.

Figure 2 is a schematic diagram of a lithium-ion battery 1 according to a first embodiment of the present disclosure.

As shown in FIG. 2, the lithium-ion battery 1 has a positive electrode current collector layer 11, a positive electrode active material layer 12, a solid electrolyte layer 13, a negative electrode active material layer 14, and a negative electrode current collector layer 15 stacked in this order. At least one of the positive electrode active material layer 12 and the negative electrode active material layer 14 is an electrode active material layer according to the present disclosure.

<Positive electrode current collector layer>
The material used for the positive electrode current collector layer may be, but is not limited to, stainless steel (SUS), aluminum, copper, nickel, iron, titanium, carbon, etc. Among these, the material for the positive electrode current collector layer is preferably aluminum.

The shape of the positive electrode current collector layer is not particularly limited, and examples include foil, plate, and mesh. Of these, foil is preferred.

<Cathode active material layer>
When the electrode active material layer of the present disclosure is not a positive electrode active material layer, the positive electrode active material layer of the lithium ion battery of the present disclosure contains a positive electrode active material and, optionally, a solid electrolyte. In addition, depending on the intended use and purpose, the positive electrode active material layer may contain additives used in the positive electrode active material layer of a lithium ion battery, such as a conductive additive or a binder. The solid electrolyte may be a sulfide solid electrolyte.

When the electrode active material layer of the present disclosure is not a positive electrode active material layer, the positive electrode active material layer may contain any positive electrode active material that can be used in a lithium-ion battery.

Such a positive electrode active material may be, for example, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , or a different element-substituted Li-Mn spinel having a composition represented by Li _1+x Mn _2-x-y M _y O ₄ (M is one or more metal elements selected from Al, Mg, Co, Fe, Ni, and Zn), but is not limited to these.

Furthermore, such a positive electrode active material may be, for example, a sulfur-based active material. Here, the sulfur-based active material is an active material containing at least an S element. The sulfur-based active material may or may not contain an Li element. Examples of sulfur-based active materials include elemental sulfur, lithium sulfide (Li ₂ S), and lithium polysulfide (Li ₂ S _x , 2≦x≦8).

The solid electrolyte may be one described in the "Sulfide Solid Electrolyte" section of the "Electrode Composite" section. However, if the electrode active material layer of the present disclosure is not a positive electrode active material layer, the positive electrode active material layer may use another solid electrolyte, such as an oxide solid electrolyte.

The conductive additives and binders described in the "Electrode Mixture" section can be used.

<Solid electrolyte layer>
The solid electrolyte layer contains a solid electrolyte and, optionally, a binder.

The solid electrolyte may be one of those described in "Sulfide Solid Electrolyte" under "Electrode Composite," but may be any solid electrolyte commonly used in lithium-ion secondary batteries. In particular, it is preferable that the solid electrolyte be a sulfide solid electrolyte.

<Negative electrode active material layer>
When the electrode active material layer of the present disclosure is not a negative electrode active material layer, the negative electrode active material layer of the lithium ion battery of the present disclosure contains a negative electrode active material and, optionally, a solid electrolyte. In addition, depending on the intended use and purpose, the negative electrode active material layer may contain additives used in the negative electrode active material layer of a lithium ion battery, such as a conductive additive or a binder. The solid electrolyte may be a sulfide solid electrolyte.

When the electrode active material layer of the present disclosure is not a negative electrode active material layer, the negative electrode active material layer may contain any negative electrode active material that can be used in a lithium-ion battery.

Such a negative electrode active material may be, for example, metallic lithium, or a material capable of absorbing and releasing metal ions such as lithium ions. Examples of materials capable of absorbing and releasing metal ions such as lithium ions include, but are not limited to, alloy-based negative electrode active materials or carbon materials.

The alloy-based negative electrode active material is not particularly limited and may, for example, be a Si alloy-based negative electrode active material or a Sn alloy-based negative electrode active material. Examples of Si alloy-based negative electrode active materials include silicon, silicon oxide, silicon carbide, silicon nitride, and solid solutions thereof. Si alloy-based negative electrode active materials may also contain elements other than silicon, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti. Examples of Sn alloy-based negative electrode active materials include tin, tin oxide, tin nitride, and solid solutions thereof. Sn alloy-based negative electrode active materials may also contain elements other than tin, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Ti, and Si. Among these, Si alloy-based negative electrode active materials are preferred.

The carbon material is not particularly limited, and examples include hard carbon, soft carbon, and graphite.

The solid electrolyte may be one described in the "Sulfide Solid Electrolyte" section of the "Electrode Composite" section. However, if the electrode active material layer of the present disclosure is not a negative electrode active material layer, the negative electrode active material layer may use another solid electrolyte, such as an oxide solid electrolyte.

The conductive additives and binders described in the "Electrode Mixture" section can be used.

<Negative electrode current collector layer>
The material used for the negative electrode current collector layer may be the same as the material used for the positive electrode current collector layer, but is preferably copper.

Examples 1 to 3 and Comparative Examples 1 and 2
Example 1
A polymer having norbornene-derived monomer units and maleic anhydride-derived monomer units was mixed with diisobutyl ketone in an amount 6.16 times by weight of the polymer, and stirred with a stirrer for 10 hours. LiTFSI was then added in an amount 0.4 times by weight, and the mixture was stirred with a stirrer (Corning PC-420D) to prepare a polymer electrolyte solution.

The molar ratio of maleic anhydride-derived monomer units to norbornene-derived monomer units in the polymer was __%. The number average molecular weight of the polymer was __.

944 mg of the above polymer solution (176 mg in terms of polymer electrolyte), 267 mg of DIBK, 400 mg of negative electrode active material (Si particles), 32 mg of conductive additive (VGCF), and an appropriate amount of DIBK were added to a polypropylene (PP) container and stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). The mixture was then shaken for 30 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.).

This resulted in the preparation of the negative electrode composite slurry for Example 1.

The prepared negative electrode mixture slurry was applied to the negative electrode current collector layer (Cu foil) using an applicator by the blade method, and then dried on a hot plate at 100°C for 30 minutes.

This formed a negative electrode active material layer on the negative electrode current collector layer.

A positive electrode active material (LiNiCoAlO ₂ , average particle size D50 = 6 μm) with a LiNbO ₃ coating on its surface was prepared. A butyl butyrate solution containing 5 wt% butyl butyrate and a PVDF-based binder, the positive electrode active material, a sulfide solid electrolyte material (Li ₂ S-P ₂ S ₅ -based glass ceramics), and a conductive additive (VGCF) were added to a polypropylene (PP) container and stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). The mixture was then shaken for 3 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.).

This prepared the positive electrode composite slurry.

The prepared positive electrode mixture slurry was applied to a positive electrode current collector (Al foil, manufactured by Showa Denko K.K.) using an applicator by the blade method, and then dried on a hot plate at 100°C for 30 minutes. This formed a positive electrode active material layer on the positive electrode current collector layer.

Next, heptane, a heptane solution containing 5% by weight of a butylene rubber (BR)-based binder, and a sulfide solid electrolyte material (Li2S-P2S5-based glass ceramics) were added to a polypropylene (PP) container and stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT Corporation). The mixture was then shaken for 30 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.).

This resulted in the preparation of a solid electrolyte slurry.

The prepared solid electrolyte slurry was applied to a substrate (Al foil) using an applicator by the blade method, and then dried on a hot plate at 100°C for 30 minutes.

This resulted in the formation of a solid electrolyte layer on the substrate.

A positive electrode active material layer formed on a positive electrode current collector layer and a solid electrolyte layer formed on a substrate were laminated so that the positive electrode active material layer and the solid electrolyte layer were in contact with each other. A pressure of 600 MPa was applied to this positive electrode current collector layer-positive electrode active material layer-solid electrolyte layer-substrate laminate, and then the substrate was peeled off from the solid electrolyte layer to obtain a positive electrode current collector layer-positive electrode active material layer-solid electrolyte layer laminate.

Next, the negative electrode active material layer formed on the negative electrode current collector layer and the solid electrolyte layer formed on the substrate were laminated so that the negative electrode active material layer and the solid electrolyte layer were in contact with each other. A pressure of 30 kN/cm was applied to this negative electrode current collector layer-negative electrode active material layer-solid electrolyte layer-substrate laminate using a roll press, and then the substrate was peeled off from the solid electrolyte layer to obtain a negative electrode current collector layer-negative electrode active material layer-solid electrolyte layer laminate.

A pressure of 40 MPa was applied to the solid electrolyte layer of the negative electrode current collector layer-negative electrode active material layer-solid electrolyte layer laminate, which was then laminated on the solid electrolyte layer of the positive electrode current collector layer-positive electrode active material layer-solid electrolyte layer laminate obtained in this manner, to prepare an all-solid-state lithium ion secondary battery cell (all-solid-state battery).

Example 2
A polymer electrolyte solution was prepared in the same manner as in Example 1.

Then, 479 mg of the polymer solution (89 mg in terms of polymer electrolyte), 267 mg of DIBK, 400 mg of negative electrode active material (Si particles), 146 mg of sulfide solid electrolyte material (Li ₂ S-P ₂ S ₅ -based glass ceramics), 32 mg of conductive additive (VGCF), and an appropriate amount of DIBK were added to a polypropylene (PP) container, and the mixture was stirred for 30 seconds with an ultrasonic disperser (UH-50 manufactured by SMT). Then, the mixture was shaken for 30 minutes with a shaker (TTM-1 manufactured by Shibata Scientific Co., Ltd.).

This resulted in the preparation of the negative electrode composite slurry for Example 2.

The rest of the procedure was the same as in Example 1, and the all-solid-state battery of Example 2 was prepared.

Example 3
A slurry of the negative electrode mixture of Example 3 was prepared in the same manner as in Example 2, except that the amount of the sulfide solid electrolyte material was 245 mg.

The rest of the procedure was the same as in Example 1, and the all-solid-state battery of Example 3 was prepared.

Comparative Example 1
A polypropylene (PP) container was charged with a butyl butyrate solution containing butyl butyrate and a PVDF binder at a ratio of 5 wt%, 600 mg of negative electrode active material (Si particles), 466 mg of sulfide solid electrolyte material (Li ₂ S-P ₂ S ₅ -based glass ceramics), and 48 mg of conductive additive (VGCF), and the mixture was stirred for 30 seconds with an ultrasonic disperser (UH-50 manufactured by SMT). The mixture was then shaken for 30 minutes with a shaker (TTM-1 manufactured by Shibata Scientific Co., Ltd.).

This resulted in the preparation of the negative electrode composite slurry for Comparative Example 1.

The rest of the procedure was the same as in Example 1, and an all-solid-state battery of Comparative Example 1 was prepared.

Comparative Example 2
Diisobutyl ketone was added to polyvinylidene fluoride (PVDF: HSV900 manufactured by Arkema) in an amount 8 times by weight of the PVDF, and the mixture was stirred with a stirrer for 10 hours. LiTFSI was then added in an amount 1.5 times by weight, and the mixture was stirred with a stirrer (PC-420D manufactured by Corning Incorporated) to prepare a polymer electrolyte solution.

800 mg of the above polymer solution, DIBK, 400 mg of negative electrode active material (Si particles), and 32 mg of conductive additive (VGCF) were added to a polypropylene (PP) container and stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). The mixture was then shaken for 30 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.).

This resulted in the preparation of the negative electrode slurry for Comparative Example 2.

The rest of the procedure was the same as in Example 1, and an all-solid-state battery of Comparative Example 2 was prepared.

Battery evaluation
The all-solid-state battery of each example was charged at 0.1 C by constant current-constant voltage (CC-CV) to 4.2 V. Then, CC-CV discharge was performed at 0.1 C to 2.7 V. During this charging, the discharge capacity was obtained and the confining pressure of the all-solid-state battery was monitored, and the confining pressure of the all-solid-state battery at 4.2 V was measured and compared with the confining pressure of the all-solid-state batteries of Comparative Examples 1 and 2 and Example 1.

The charging and discharging was then repeated under the same conditions, which was considered the second charging and discharging.

Note that the pressure increase rate (MPa/mAh) for the all-solid-state battery of Comparative Example 1 during the first charge was set at 100, and the relative values were compared.

Furthermore, the discharge capacities (mAh) during the first and second discharges were compared relative to the discharge capacity of the all-solid-state battery of Comparative Example 1, which was set at 100.

<result>
The configuration of each example and the evaluation results of the battery are shown in Table 1. In Table 1, "norbornene/maleic anhydride" means a polymer having a monomer unit derived from norbornene and a monomer unit derived from maleic anhydride.

As shown in Table 1, in Comparative Example 1, in which the electrolyte in the negative electrode active material layer was only a sulfide solid electrolyte, the pressure increase rate in the all-solid-state battery of Comparative Example 1 during the first charge was smaller in Comparative Example 2 and Example 1, in which the electrolyte in the negative electrode active material layer contained a polymer electrolyte. In particular, in Example 1, in which the polymer electrolyte contained a polymer having a norbornene-derived monomer unit and a maleic anhydride-derived monomer unit, the pressure increase rate was 85, which was particularly small.

In addition, Examples 2 and 3, in which the electrolyte in the negative electrode active material layer contained a sulfide solid electrolyte and the polymer electrolyte contained a polymer having a norbornene-derived monomer unit and a maleic anhydride-derived monomer unit, had second discharge capacities of 101 and 96, respectively, which were greater than the second discharge capacity of Example 1, in which the electrolyte in the negative electrode active material layer did not contain a sulfide solid electrolyte.

REFERENCE SIGNS LIST 1 Lithium ion battery 11 Positive electrode current collector layer 12 Positive electrode active material layer 13 Solid electrolyte layer 14 Negative electrode active material layer 15 Negative electrode current collector layer

Claims (3)

A lithium ion battery having a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer stacked in this order,
The negative electrode active material layer is
Si or Sn, or alloy-based active material,
The battery contains a polymer electrolyte having a monomer unit derived from a norbornene and a monomer unit derived from a maleic anhydride, and a sulfide solid electrolyte,
the ratio of the mass of the polymer electrolyte to the total mass of the polymer electrolyte and the sulfide solid electrolyte is 20.0 to 40.0 mass% ,
the positive electrode active material layer contains the sulfide solid electrolyte and does not contain the polymer electrolyte; and
The solid electrolyte layer contains the sulfide solid electrolyte.
Lithium-ion battery . 2. The lithium ion battery according to claim 1 , wherein a molar ratio of the monomer units derived from maleic anhydrides to the monomer units derived from norbornenes in the polymer electrolyte is 40 to 60%. 3. The lithium ion battery according to claim 1 , wherein the polymer electrolyte has an average molecular weight of 5,000 to 50,000.